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JunosE 11.3.x IP, IPv6, and IGP Configuration Guide
How ARP Works
18
NOTE: For information about MAC address validation, see "MAC Address
Validation" on page 21.
Figure 8 on page 18 and Figure 9 on page 19 show how ARP works where host 1 sends
an IP packet to host 2 on a different subnet. To complete this transmission, host 1 needs
the MAC address of router 1, to be used as the forwarding gateway.
A typical scenario is:
Host 1 broadcasts an ARP request to all devices on subnet 1, composed by a query
1.
with the IP address of router 1. The IP address of router 1 is needed because host 2 is
on a different subnet.
All devices on subnet 1 compare their IP address with the enclosed IP address sent
2.
by host 1.
Having the matching IP address, router 1 sends an ARP response, which includes its
3.
MAC address, to host 1.
Figure 8: Sample ARP Process—1 through 3
Host 1 transmits the IP packet to layer 3 DA (host 2) using router 1's MAC address.
4.
Router 1 forwards IP packet to host 2. Router 1 might send an ARP request to identify
5.
the MAC of host 2. (See Figure 9 on page 19.)
Copyright © 2010, Juniper Networks, Inc.
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